The Collaborative International Dictionary of English v.0.48:

Sketchbook \Sketch"book`\, n.
   A book of sketches or for sketches.
   [1913 Webster]

WordNet (r) 3.0 (2006):

sketchbook
    n 1: a book containing sheets of paper on which sketches can be
         drawn [syn: sketchbook, sketch block, sketch pad]

Moby Thesaurus II by Grady Ward, 1.0:

71 Moby Thesaurus words for "sketchbook":
   air brush, art paper, best seller, book, bound book, brush,
   camera lucida, camera obscura, canvas, chalk, charcoal, classic,
   coloring book, crayon, definitive work, drawing paper,
   drawing pencil, drier, easel, fixative, folio, great work, ground,
   hardback, juvenile, juvenile book, lay figure, limp-cover book,
   magnum opus, maulstick, medium, nonbook, notebook, novel, opus,
   opuscule, opusculum, paint, paintbrush, palette, palette knife,
   paperback, pastel, pencil, picture book, pigments, playbook,
   pocket book, prayer book, production, psalmbook, psalter,
   publication, scratchboard, serial, siccative, sketchpad,
   soft-cover, songbook, spatula, spray gun, standard work, storybook,
   stump, title, tome, trade book, varnish, volume, work, writing